The present invention provides a novel S(+) isomer of desmethylselegiline, i.e., a compound of the formula: 
and further provides novel pharmaceutical and other compositions containing this isomer. In addition, the present invention provides novel methods for using this enantiomer in the treatment of selegiline-responsive diseases and conditions in animals, including humans.
Two distinct monoamine oxidase enzymes are known in the art: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). The cDNAs encoding these enzymes show different promoter regions and distinct exon portions, indicating they are encoded independently at different gene positions. In addition, analysis of the two proteins has shown differences in their respective amino acid sequences.
The first compound found to selectively inhibit MAO-B was R-(xe2x88x92)-N-methyl-N-(prop-2-ynyl)-2-aminophenylpropane, also known as L-(xe2x88x92)-deprenyl, R-(xe2x88x92)-deprenyl, or selegiline. Selegiline has the following structural formula: 
The selectivity of selegiline in the inhibition of MAO-B is important to its safety profile following oral administration. Inhibition of MAO-A may cause toxic side effects by interfering with the metabolism of tyramine. Tyramine is normally metabolized in the gastrointestinal tract by MAO-A but when MAO-A is inhibited, tyramine absorption is increased following consumption of tyramine-containing foods such as cheese, beer, herring, etc. This results in the release of catecholamines which can precipitate a hypertensive crisis, producing the xe2x80x9ccheese effect.xe2x80x9d This effect is characterized by Goodman and Gilman as the most serious toxic effect associated with MAO-A inhibitors.
One of the metabolites of selegiline is its N-desmethyl analog. Structurally, desmethylselegiline is the R(xe2x88x92) enantiomeric form of a secondary amine of the formula: 
Heretofore, desmethylselegiline was not known to have pharmaceutically useful MAO-related effects, i.e., potent and selective inhibitory effects on MAO-B. In the course of determining the usefulness of desmethylselegiline for the purposes of the present invention, the MAO-related effects of desmethylselegiline were more completely characterized. This characterization has established that desmethylselegiline has exceedingly weak MAO-B inhibitory effects and no advantages in selectivity with respect to MAO-B compared to selegiline.
For example, the present characterization established that selegiline has an IC50 value against MAO-B in human platelets of 5xc3x9710xe2x88x929 M whereas R(xe2x88x92)desmethylselegiline""s IC50 value is 4xc3x9710xe2x88x927 M, indicating the tatter is approximately 80 times less potent as an MAO-B inhibitor than the former. Similar characteristics can be seen in the following data measuring inhibition of MAO-B and MAO-A in rat cortex mitochondrial-rich fractions:
As is apparent from the above table, selegiline is approximately 128 times more potent as an inhibitor of MAO-B relative to MAO-A, whereas desmethylselegiline is about 97 times more potent as an inhibitor of MAO-B relative to MAO-A. Accordingly, desmethylselegiline appears to have an approximately equal selectivity for MAO-B compared to MAO-A as selegiline, albeit with a substantially reduced potency.
Analogous results are obtained in rat brain tissue. Selegiline exhibits an IC50 for MAO-B of 0.11xc3x9710xe2x88x927 M whereas desmethylselegiline""s IC50 value is 7.3xc3x9710xe2x88x927 M, indicating desmethylselegiline is approximately 70 times less potent as an MAO-B inhibitor than selegiline. Both compounds exhibit low potency in inhibiting MAO-A in rat brain tissue, 0.18xc3x9710xe2x88x925 for selegiline, 7.0xc3x9710xe2x88x925 for desmethylselegiline. Thus, in vitro R(xe2x88x92)desmethylselegiline is approximately 39 times less potent than selegiline in inhibiting MAO-A.
Based on its pharmacological profile as set forth above, R(xe2x88x92)desmethylselegiline as an MAO-B inhibitor provides no advantages in either potency or selectivity compared to selegiline. To the contrary, the above in vitro data suggest that use of desmethylselegiline as an MAO-B inhibitor requires on the order of 70 times the amount of selegiline.
The potency of desmethylselegiline as an MAO-B inhibitor in vivo has been reported by Heinonen, E. H., et al. (xe2x80x9cDesmethylselegiline, a metabolite of selegiline, is an irreversible inhibitor of MAO-B in human subjects,xe2x80x9d referenced in Academic Dissertation xe2x80x9cSelegiline in the Treatment of Parkinson""s Disease,xe2x80x9d from Research Reports from the Department of Neurology, University of Turku, Turku, Finland, No. 33 (1995), pp. 59-61). According to Heinonen, desmethylselegiline in vivo has only about one-fifth the MAO-B inhibitory effect as selegiline, i.e., a dose of 10 mg of desmethylselegiline would be required for the same MAO-B effect as 1.8 mg of selegiline. In rats, Barbe reported R(xe2x88x92)desmethylselegiline to be an irreversible inhibitor of MAO-B, with a potency about 60 fold lower than selegiline in vitro and about 3 fold lower ex vivo (Barbe, H. O., J. Neural Trans. (Suppl.):32:131 (1990)).
The various diseases and conditions for which selegiline is disclosed as being to be useful include: depression (U.S. Pat. No. 4,861,800); Alzheimer""s disease and Parkinson""s disease, particularly through the use of transdernal dosage forms, including ointments, creams and patches; macular degeneration (U.S. Pat. No. 5,242,950); age-dependent degeneracies, including renal function and cognitive function as evidenced by spatial learning ability (U.S. Pat. No. 5,151,449); pituitary-dependent Cushing""s disease in humans and nonhumans (U.S. Pat. No. 5,192,808); immune system dysfunction in both humans (U.S. Pat. No. 5,387,615) and animals (U.S. Pat. No. 5,276,057); age-dependent weight loss in mammals (U.S. Pat. No. 5,225,446); and schizophrenia (U.S. Pat. No. 5,151,419). PCT Published Application WO 92/17169 discloses the use of selegiline in the treatment of neuromuscular and neurodegenerative disease and in the treatment of CNS injury due to hypoxia, hypoglycemia, ischemic stroke or trauma. In addition, the biochemical effects of selegiline on neuronal cells have been extensively studied. For example, see Tatton, et al., xe2x80x9cSelegiline Can Mediate Neuronal Rescue Rather than Neuronal Protection,xe2x80x9d Movement Disorders 8 (Supp. 1):S20-S30 (1993); Tatton, et al., xe2x80x9cRescue of Dying Neurons,xe2x80x9d J. Neurosci. Res. 30:666-672 (1991); and Tatton, et al., xe2x80x9c(xe2x88x92)-Deprenyl Prevents Mitochondrial Depolarization and Reduces Cell Death in Trophically-Deprived Cells,xe2x80x9d 11th Int""l Symp. on Parkinson""s Disease, Rome, Italy, Mar. 26-30, 1994.
Although selegiline is reported as being effective in treating the foregoing conditions, neither the precise number or nature of its mechanism or mechanisms of action are known. However, there is evidence that selegiline provides neuroprotection or neuronal rescue, possibly by reducing oxidative neuronal damage, increasing the amount of the enzyme superoxide dismutase, and/or reducing dopamine catabolism. For example, PCT Published Application WO 92/17169 reports that selegiline acts by directly maintaining, preventing loss of, and/or assisting in, the nerve function of animals.
Selegiline is disclosed as being useful when administered to a subject through a wide variety of routes of administration and dosage forms. For example U.S. Pat. No. 4,812,481 (Degussa AG) discloses the use of concomitant selegiline-amantadine in oral, peroral, enteral, pulmonary, rectal, nasal, vaginal, lingual, intravenous, intraarterial, intracardial, intramuscular, intraperitoneal, intracutaneous, and subcutaneous formulations. U.S. Pat. No. 5,192,550 (Alza Corporation) describes a dosage form comprising an outer wall impermeable to selegiline but permeable to external fluids. This dosage form may have applicability for the oral, sublingual or buccal administration of selegiline. Similarly, U.S. Pat. No. 5,387,615 discloses a variety of selegiline compositions, including tablets, pills, capsules, powders, aerosols, suppositories, skin patches, parenterals, and oral liquids, including oil-aqueous suspensions, solutions, and emulsions. Also disclosed are selegiline-containing sustained release (long acting) formulations and devices.
The present invention is directed to the novel, S(+) enantiomeric form of desmethylselegiline. This isomer has striking and wholly unexpected pharmacological effects and, accordingly, is surprisingly and unexpectedly useful in treating selegiline-responsive diseases and conditions. Assay results suggest that, in at least some respects, the S(+) enantiomer is considerably more effective than either selegiline or the R(xe2x88x92) enantiomer of desmethylselegiline. For example, results suggest that the S(+) enantiomer may be 4-5 times more effective than these other agents at inhibiting dopamine re-uptake by neurons and, in certain cell culture models, it has a greater neuroprotective effect than either R(xe2x88x92)desmethylselegiline or selegiline. Thus, the S(+) isomer is the form of choice in the treatment of conditions which require enhanced synaptic dopamine activity or neuronal protection/rescue. Such conditions include Parkinson""s disease; Alzheimer""s disease and attention deficit hyperactivity disorder (ADHD); dementia; depression; schizophrenia; and dysautonomia.
The present invention provides in part:
(a) a composition comprising the S(+) enantiomer of desmethylselegiline, a compound of the formula: 
including the S(+) enantiomer in substantially isomerically pure form;
(b) a pharmaceutical composition comprising the S(+) enantiomer of desmethylselegiline, wherein one or more unit doses of said composition, administered on a periodic basis, are effective to treat a selegiline-responsive disease or condition in a animal to whom said unit dose or unit doses are administered;
(c) in a method for obtaining a selegiline-like therapeutic effect in a subject suffering from a selegiline-responsive disease or condition, the improvement which comprises:
administering to said subject the S(+) enantiomer of desmethylselegiline in a dosage regimen sufficient to produce said selegiline-like therapeutic effect.
(d) a method of treating a condition in a mammal produced by neuronal degeneration, neuronal trauma or by a hypodopaminergic condition which comprises administering to said mammal the S(+) enantiomer of desmethylselegiline or a pharmaceutically acceptable acid addition salt thereof, at a daily dose, administered in a single or multiple dosage regimen, of at least about 0.015 mg, calculated on the basis of the free secondary amine, per kg of the mammal""s body weight;
(e) a transdermal delivery composition for use in treating a condition in a mammal produced by neuronal degeneration, neuronal trauma or due to a hypodopaminergic condition which comprises a layered composite containing in at least one layer an amount of the S(+) enantiomer of desmethylselegiline, or a pharmaceutically acceptable acid addition salt thereof, sufficient to supply a daily transdermal dose of at least about 0.015 mg of the free secondary amine, per kg of the mammal""s body weight; and
(f) a method of treating a condition in a mammal produced by immune system dysfunction, which comprises administering to the mammal the S(+) enantiomer of desmethylselegiline, or a pharmaceutically acceptable acid addition salt thereof, at a daily dose, administered in a single or multiple dosage regimen, of at least about 0.015 mg, calculated on the basis of the free secondary amine, per kg of the mammal""s body weight.
The present invention is based upon the discovery that both desmethylselegiline (xe2x80x9cDMSxe2x80x9d or xe2x80x9cR(xe2x88x92)DMSxe2x80x9d) and its enantiomer (ent-desmethylselegiline, abbreviated as xe2x80x9cent-DMSxe2x80x9d or xe2x80x9cS(+)DMSxe2x80x9d) are useful in providing selegiline-like effects in subjects, notwithstanding dramatically reduced MAO-B inhibitory activity and an apparent lack of enhanced selectivity for MAO-B compared to selegiline. It has been discovered that desmethylselegiline, ent-desmethylselegiline and their isomeric mixtures provide a more advantageous way of obtaining selegiline-like therapeutic effects in selegiline-responsive diseases or conditions. This, is particularly true for diseases or conditions characterized by neuronal degeneration, neuronal trauma or which are hypodopaminergic in nature, i.e. diseases or conditions characterized by reduced dopamine release and formation.
Thus, the present invention is directed to compositions comprising the S(+) enantiomer of desmethylselegiline either alone or together with the R(xe2x88x92) enanatiomer. In preferred embodiments, the S(+) enantiomer is present at a greater concentration than the concentration of the R(xe2x88x92) enantiomer or, alternatively, in substantially isomerically pure form. S(+) and R(xe2x88x92) forms of desmethylselegiline can be conveniently prepared by methods known in the art, as described below in Example 1. The characteristics of a preparation of purified S(+) enantiomer have been determined and are described in Example 3. Its chemical structure is as follows: 
The S(+) enantiomer, S(+)DMS, is used as an active ingredient in novel pharmaceutical compositions. In this regard, a quantity of the isomer is employed such that one or more unit doses of the composition is effective in the treatment of one or more selegiline-responsive diseases or conditions in a subject administered the composition on a periodic basis. If desired, the R(xe2x88x92) enantiomer may be included. Compositions may be designed so that they are suitable for oral, topical, transdermal, sublingual, buccal, parenteral or other conventional routes of administration. So formulated and administered, S(+)DMS compositions are useful for effecting an increase in dopaminergic activity, neuronal rescue/protection and can be administered in a manner so as to improve immune system function in a subject or to treat hypodopaminergic related diseases.
In addition, the present invention provides for an improved method for obtaining a selegiline-like therapeutic effect in a subject suffering from a selegiline-responsive disease or condition, which comprises administering to the subject the S(+) enantiomer of desmethylselegiline in an amount sufficient to produce the selegiline-like therapeutic effect. The S(+)DMS may be present in substantially isomerically pure form, a form preferred for the treatment of ADHD, or it may be present together with R(xe2x88x92)DMS.
As used herein the term xe2x80x9cselegiline-responsive disease or conditionxe2x80x9d refers to any of the various diseases or conditions in mammals, including humans, for which selegiline is disclosed in the prior art as being useful. In particular, a xe2x80x9cselegiline-responsive disease or conditionxe2x80x9d refers to the various diseases and conditions described above, e.g., Alzheimer""s disease, cognitive dysfunction, neuronal rescue or protection, and the like. The term also refers to the use of selegiline as an appetite suppressant. Similarly, the term xe2x80x9cselegiline-like therapeutic effectxe2x80x9d refers to one or more of the salutary effects reported as being exerted by selegiline in subjects being treated for a selegiline-responsive disease or condition.
The selegiline-responsive diseases or conditions related to neuronal degeneration or trauma which respond to the present methods include Parkinson""s disease, Alzheimer""s disease, depression, glaucoma, macular degeneration, ischemia, diabetic neuropathy, attention deficit disorder, post polio syndrome, multiple sclerosis, impotence, narcolepsy, chronic fatigue syndrome, alopecia, senile dementia, hypoxia, cognitive dysfunction, negative symptomatology of schizophrenia, amyotrophic lateral sclerosis, Tourette""s syndrome, tardive dyskinesia, and toxic neurodegeneration.
In preferred embodiments, the invention is directed to a method of treating a mammal for a hypodopatninergic condition or neuronal trauma/neuronal degeneration by administering the S(+) enantiomer of desmethylselegiline, or a pharmaceutically acceptable acid addition salt of this enantiomer, at a daily dose of at least about 0.015 mg per kg body weight. The dosage is based upon the weight of the free secondary amine and may be administered in either a single or multiple dosage regimen.
The present invention also encompasses the restoration or improvement of immune system function by S(+)DMS. Again, the S(+) enantiomer may be administered either as a substantially pure isomer or in combination with R(xe2x88x92)DMS. The conditions or diseases treatable include age-dependent immune system dysfunction, AIDS, immunological loss due to cancer chemotherapy and infectious diseases. In a preferred embodiment, the invention is directed to a method of treating a condition in a mammal produced by immune system dysfunction, by administering the S(+) enantiomer of desmethyl-selegiline, or a pharmaceutically acceptable acid addition salt thereof, at a daily dose of at least about 0.015 mg, calculated on the basis of the free secondary amine, per kg of the mammal""s body weight.
Depending upon the particular route employed, desmethylselegiline is administered in the form of a free base or as a physiologically acceptable non-toxic acid addition salt. Acid addition salts include those derived from organic and inorganic acids such as, without limitation, hydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid, methanesulphonic acid, acetic acid, tartaric acid, lactic acid, succinic acid, citric acid, malic acid, maleic acid, sorbic acid, aconitic acid, salicylic acid, phthalic acid, embonic acid, enanthic acid, and the like. The use of salts, especially the hydrochloride, is particularly desirable when the route of administration employs aqueous solutions, as for example parenteral administration. Use of delivered S(+)desmethylselegiline, in the form of the free base is especially useful for transdermal administration. Reference herein to the administration of DMS or ent-DMS or to mixtures thereof encompasses both the free base and acid addition salt forms.
The optimal daily dose of S(+)-desmethylselegiline useful for the purposes of the present invention is determined by methods known in the art, e.g., based on the severity of the disease or condition being treated, the condition of the subject to whom treatment is being given, the desired degree of therapeutic response, and the concomitant therapies being administered to the patient or animal. Ordinarily, however, the attending physician or veterinarian will administer an initial dose of at least about 0.015 mg/kg, calculated on the basis of the free secondary amine, with progressively higher doses being employed depending upon the route of administration and the subsequent response to the therapy. Typically the daily dose will be about 0.10 mg/kg and may extend to about 1.0 mg/kg of the patient""s body weight (all such doses again being calculated on the basis of the free secondary amine). These guidelines further require that the actual dose be carefully titrated by the attending physician or veterinarian depending on the age, weight, clinical condition, and observed response of the individual patient or animal.
The daily dose can be administered in a single or multiple dosage regimen. Oral dosage forms will most typically be used and are preferred but other dosage forms may also be employed and may permit, for example, a continuous release of relatively small amounts of the active ingredient from a single dosage unit, such as a transdermal patch, over the course of one or more days. This is particularly desirable in the treatment of chronic conditions such as Parkinson""s disease, Alzheimer""s disease, and depression. Alternatively, it may be desirable in conditions such as ischemia or neural damage to administer one or more discrete doses by a more direct systemic route such as intravenously or by inhalation. In still other instances such as glaucoma and macular degeneration, localized administration, such as via the intraocular route, can be indicated.
Pharmaceutical compositions containing S(+)-desmethylselegiline can be prepared according to conventional techniques. For example, preparations for parenteral routes of administration of S(+)-desmethylselegiline, e.g., intramuscular, intravenous and intraarterial routes, can employ sterile isotonic saline solutions. Sterile isotonic buffered solutions can also be employed for intraocular administration.
Transdermal dosage unit forms of S(:+)-desmethylselegiline can be prepared utilizing a variety of previously described techniques (see e.g., U.S. Pat. Nos. 4,861,800; 4,868,218; 5,128,145; 5,190,763; and 5,242,950; and EP-A 404807, EP-A 509761, and EP-A 593807). For example, a monolithic patch structure can be utilized in which S(+)-desmethylselegiline is directly incorporated into the adhesive and this mixture is cast onto a backing sheet. Alternatively S(+)-desmethylselegiline, can be incorporated as an acid addition salt into a multilayer patch which effects a conversion of the salt to the free base, as described for example in EP-A 593807. In a preferred embodiment, the present invention is directed to a transdermal delivery composition for use in treating a condition in a mammal produced by neuronal degeneration or neuronal trauma and for treating hypodopaminergic diseases.
Subjects treatable by the present preparations and methods include both human and non-human subjects for which selegiline-like therapeutic effects are known to be useful. Accordingly, the compositions and methods above provide especially useful therapies for mammals, especially domesticated mammals. Thus, the present methods and compositions are used in treating selegiline-responsive diseases or conditions in canine and feline species.
Successful use of the compositions and methods above requires employment of an effective amount of S(+)-desmethylselegiline. Although both R(xe2x88x92) desmethylselegiline and S(+)-desmethylselegiline are dramatically less potent than selegiline as inhibitors of MAO, employment of these agents, or a mixture of these agents, does not require a commensurately increased dosage to obtain a selegiline-like therapeutic response. Surprisingly, dosages necessary to attain a selegiline-like therapeutic effect appear to be on the same order as the known doses of selegiline. Accordingly, because both desmethylselegiline and ent-desmethylselegiline exhibit a much lower inhibition of MAO-A at such dosages, desmethylselegiline and ent-desmethylselegiline provide a substantially wider margin of safety with respect to MAO-A associated toxicity compared to selegiline. In particular, the risk of the adverse effects of MAO-A inhibition, e.g., hypertensive crisis, are minimized due to the reduced potency for MAO-A inhibition.
As described above and notwithstanding its demonstrably inferior inhibitory properties with respect to MAO-B inhibition, S(+)desmethylselegiline appears to be at least as effective as selegiline in treating certain selegiline-responsive conditions, e.g., conditions resulting from reduced dopamine release and formation, neuronal degeneration or neuronal trauma. Although the oral route of administration will generally be most convenient, drug may be administered by the parenteral, topical, transdermal, intraocular, buccal, sublingual, intranasal, inhalation, vaginal, rectal or other routes as well.